Bone Microdamage and Its Contributions to Fracture - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 86

Fig. 1 Microdamage forms as two different morphologies. An image of a linear microcrack (top)
is shown under a bright-field microscopy, and b confocal microscopy. An image of diffuse
damage (bottom) is shown under c bright-field microscopy, and d confocal microscopy. Scale
bars = 50 lm. Reprinted with permission from Elsevier [ 8 ]
a repair process of intracortical remodeling [ 3 - 5 ]. However, there is an age-related
accumulation of microdamage in bones [ 1 , 6 ], due either to deterioration of the
repair mechanism with age [ 4 , 7 ] or to matrix changes that reduce the damage
resistance of bone.
Microdamage can take two distinct forms [ 1 , 6 , 8 ]. Two damage morphologies,
linear microcracks and diffuse damage (Fig. 1 ), result from different types of
applied loading [ 9 - 11 ]. Linear microcracks form primarily due to compressive
loading and appear as sharply defined cracks [ 10 , 12 , 13 ]. They are primarily
found in the interstitial regions of bone where they follow the lamellar interface
and stop at the cement lines of osteons [ 8 , 11 , 14 ]. On the other hand, diffuse
damage results from tensile loads [ 9 ]. It has the appearance of a spread mesh of
submicroscopic cracks [ 15 ]. Diffuse damage is closely associated with osteonal
regions in bone, and it does not follow the lamellar boundaries [ 8 ].